In order to best utilize an auditory prosthesis for speech communication, a signal processor is required which codes the speech signal into a stimulus pattern. Such signal processors in the past have fallen into two general categories:
1. Those which stimulate electrodes in regions where, according to the place-pitch theory of hearing, they would be stimulated in a normal hearing person. Stimulation occurs at rates corresponding to the frequency of vibration of that portion of the basilar membrane.
2. Those which stimulate at one or more positions in the cochlea but with a stimulus common to all electrodes and at a rate equal or proportional to the glottis pulse rate of the speech signal. Whilst speech processors which fall into category 1 provide the formant information of the speech signal, they fail to provide prosodic information. Furthermore, since the spectral energy is distributed over broad peaks, confusing percepts may be heard by the patient. Speech processors which fall into category 2 provide the prosodic information important as an aid to lip reading, but fail to provide the necessary formant frequency information.
The invention which is the subject of PCT/Au80/00016 attempted to overcome these disadvantages by providing a speech processor having an output signal in which both formant and prosodic information is present whereby the production of confusing percepts is avoided.
The speech processor of PCT/Au80/00016 is particularly adapted for use with the implantable hearing prosthesis and the associated stimulation electrode array described in Australian Patent Application Nos. Au-A 41061/78 and AU-A 46563/79 respectively.
The hearing prosthesis includes an electrode processor having an output signal in which both formant and prosodic information is present whereby the production of confusing percepts is avoided.